Shirred food casings of flexible cellulosic tubing are commonly used in the food industry for making and processing various food products such as frankfurters, sausages, or the like. Consequently, the methods of making the shirred casing articles or "sticks", and the apparatus and methods relating to the use of the shirred casing to produce a stuffed casing food product, are all well known in the art. For example, a shirred casing, a shirring method and a shirring apparatus are all described generally in U.S. Pat. No. 2,984,574. U.S. Pat. No. 3,115,668 describes a machine for stuffing a shirred casing stick to make linked sausages or frankfurters.
The advent of automatic machines for stuffing and/or linking of shirred food casings as described, for example, in U.S. Pat. No. 3,115,668, has greatly increased the production rate of sausage type products. In an automated stuffing operation, as described in the '688Patent, hollow shirred casing sticks are fed automatically and rapidly onto the stuffing horn of the stuffing machine. The horn picks up the shirred casing stick by extending through the bore of the hollow stick to the fore end of the stick. The horn then advances the stick into a chuck. The chuck grips the fore end of the stick and rotates the stick about the horn during the stuffing operation to link the stuffed casing.
It is common to have a portion of the casing turned inward into the bore of the stick in order to plug the fore end of the bore. The end closure or "plug" formed by this inturned casing performs several functions. For example, the stuffing horn pushes on the plug for advancing the stick towards the chuck. Once the stick fore end is firmly gripped by the chuck, the advancing horn pushes the plug out of the stick bore. If the plug is too firmly anchored, the force required to push the plug from the bore (hereafter referred to as the "deplug force") can exceed the tensile strength of the stick. Should this happen, the stick will lose its integrity and separate into two pieces of shirred casing connected by a length of deshirred casing. The connecting length of deshirred casing is liable to twist around the horn and cause the stick to seize on the horn. Another possible result of a high deplug force is a tearing of the casing or a "blown end" which allows the stuffing emulsion to spew from the casing.
Another function of the plug is that it closes the casing so it can be stuffed with emulsion. In this respect, the plug must be sufficiently coherent to contain the pressure of the stuffing operation until a first link is formed. However, the plug also must be easily opened so that at the end of stuffing, emulsion can be stripped from the first links in a subsequent operation as described hereinbelow.
In general, forming a closure at one end can be most uniformly and economically accomplished during the manufacturing of the shirred casing stick. To this end, various types of casing closures and methods for forming such closures are known in the art. For example, Alsys, U.S. Pat. No. 3,274,005, discloses a shirred casing having an end which is twisted closed outside of the hollow stick and which then is pulled into a position within the bore of the shirred casing. A second Alsys Patent, U.S. Pat. No. 3,383,222, discloses a shirred casing having a compressed plug end closure implanted in the fore end of the stick. Here the plug is formed by first pulling a tab of the casing laterally across the bore of the stick, inturning the tab into the end of the casing stick, and then axially compressing the inturned tab against a fixed surface with a plunger inserted into the other end of the casing stick. Sheridan et al., U.S. Pat. No. 3,892,869, likewise discloses a closure formed within the bore of a shirred stick from casing material that has been inturned into the bore and axially compressed.
In the Alsys U.S. Pat. No. '222 and Sheridan, et al. U.S. Pat. No. '869, the inturned portion of casing is asymmetrical prior to compaction inasmuch as the casing material making up the inturned portion is not uniformly distributed around the axis of the shirred stick, but is concentrated on one side of the inturned casing portion. Specifically, there is only one ply of casing material extending in a longitudinal direction along one side of the inturned portion and three plies extending along on the opposite side. When, as taught in these patents, this inturned casing portion is longitudinally compacted within the confines of the stick bore, the plies collapse one against another into accordion-type pleats which bear tightly against the inner peripheral surface of the shirred stick, and which extend across the longitudinal axis of the bore. This forms a tightly compacted plug which has a relatively symmetrical or uniform density about its axis, and which is firmly planted in the stick bore.
In contrast to the Alsys U.S. Pat. No. '222 and Sheridan et al. U.S. Pat. No. '869, U.S. Pat. No. 4,551,370 and European Patent No. 114,397 disclose an inturned portion of casing which is symmetrical about the axis of the shirred stick prior to compaction. Compaction of this symmetrical inturned portion within the bore of the shirred stick is said to result in a closure which has a more uniform density than the closure of either the Alsys U.S. Pat. No. '222 or the Sheridan et al. U.S. Pat. No. '869.
One desideratum of an end closure for the casing stick is that it be made of as short a casing length as possible. Using an excessive amount of casing from the shirred stick to form the closure means that less casing material is left in the shirred stick for stuffing. Also, it is important that the closure should not be too tightly anchored in the bore of the shirred stick or the surrounding casing could tear or otherwise break as the tightly anchored closure is forced from the fore end of the casing stick. Another desirable feature is that the closure should not be too hard. This is because at the start of the stuffing cycle, the closure is forced out of the bore of the casing stick and into a linker mechanism which has meshing components that form the stuffed casing into links. Often the closure does not properly enter the linker mechanism and if this happens, a "hard" closure is likely to damage the meshing components. However, if the closure is "soft", the meshing components are better able to accommodate and crush the material of the closure hetween them so there is less likelihood of damage to the equipment and to the casing.
The preferred closure which has the desirable features as set out above and which is able to withstand and contain the pressure of emulsion at the onset of the stuffing operation, should also be able to be stripped of emulsion at the end of the stuffing and linking operation. In this respect, a length of unstuffed casing is needed for tying one stuffed length of casing to another for subsequent processing. Also, the first few links produced are usually malformed or understuffed. Accordingly, to provide the unstuffed casing length needed for tying, and to recover, for reuse, the emulsion contained in the first few links, the operator manually squeezes the links and strips the food emulsion from the links towards the closure in a so called "milking" action. This causes the closure to unravel, unwind or otherwise open to permit the operator to squeeze the food product out of the first few links.
It should be noted that any closure which is simply twisted closed or axially compressed, such as those described hereinabove, will begin to lose its integrity responsive to the pressure of the stuffing process. Accordingly, it is important that the closure not become completely unraveled and open prior to the time a first link is formed. Otherwise a "blown end" results which sprays food emulsion from the casing and over the stuffing machine. This causes a delay in production, because the machine must be shut down and the emulsion must be cleaned from the machine in order to prevent bacterial growth. Thus, a properly formed closure will not completely unravel or otherwise open during the initial stages of the stuffing operation, but it will unravel and open responsive to the pressure of the "milking" action so that the food emulsion in the first few links can be expressed from the casing and recovered.
The end closure of the present invention exhibits all the desirable features in that:
(1) it does not require an excessive amount of casing and is easily formed;
(2) it provides a "soft" plug which, if it becomes entangled within the linker mechanism, is not likely to cause damage;
(3) it is not tightly anchored in the stick bore and is expelled at the onset of stuffing without damaging the shirred stick;
(4) it is able to contain the pressure of the food emulsion at the onset of stuffing; and
(5) it is easily unraveled during the stripping or "milking" operation at the end of stuffing.
A still further desirable feature of the present invention is that the end closure can be made so that the tightness of its implantation in the bore of the casing stick is controllable. Heretofore, the deplugging force depended upon such variables as the length of casing contained in the plug and the force applied to compact the casing to form the plug. Modifying the deplugging force to fit the needs of a customer required an empirical balancing of these variables. For example, decreasing the length of casing in the plug might lower the deplugging force, but it also reduces the ability of the plug to contain the pressure of the food emulsion at the onset of stuffing. Increasing the compaction force might anchor the plug more securely in the casing bore, but it increases both the hardness of the plug and the risk of damage to the linker mechanism.
As a general rule, the deplug force should be as low as possible without compromising the other desirable characteristics of an end closure. In the present invention, however, once the lowest deplug force is established, the deplugging force can be raised to meet a customer's needs as dictated by his process and equipment parameters, without changing either the length of casing in the plug or the compaction force.